Despite the seeming fragmentation of the field of International Relations (IR), a theoretical common ground – not yet clearly perceived in the field – may in fact exist. Justin Rosenberg suggests that existing IR theories can all be conceived of as theories of ‘multiplicity’. This article carefully considers this proposition. It is argued that we may indeed read many IR theories as theories of multiplicity. Yet, in so doing we need to recognize the wide range of – and the contested nature of – perspectives on multiplicity in the field. Crucially, this leads us to conceive of multiplicity in an expanded way, beyond Rosenberg’s notion of ‘societal multiplicity’. Developing this more contested and expanded notion of multiplicity has important implications: for how we perceive IR and its limits in the years to come and, crucially, for the kind of trans-disciplinary dialogues IR scholars will engage in.